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| <html xmlns="http://www.w3.org/1999/xhtml"><head><title>ChaCha (bitgenerators.Bitgen.ChaCha)</title><meta charset="utf-8"/><link rel="stylesheet" href="../../../odoc.support/odoc.css"/><meta name="generator" content="odoc 2.4.1"/><meta name="viewport" content="width=device-width,initial-scale=1.0"/><script src="../../../odoc.support/highlight.pack.js"></script><script>hljs.initHighlightingOnLoad();</script></head><body class="odoc"><nav class="odoc-nav"><a href="../index.html">Up</a> – <a href="../../index.html">bitgenerators</a> » <a href="../index.html">Bitgen</a> » ChaCha</nav><header class="odoc-preamble"><h1>Module <code><span>Bitgen.ChaCha</span></code></h1><p>ChaCha is a 64-bit PRNG that uses a counter-based design based on the ChaCha cipher. Instances using different values of the key produce sequences. ChaCha has a period of <code class="odoc-katex-math">2^{128}</code> and supports arbitrary advancing and jumping the sequence in increments of <code class="odoc-katex-math">2^{64}</code>. These features allow multiple non-overlapping sequences to be generated.</p><p>The ChaCha state vector consists of a 16-element array of uint32 that capture buffered draws from the distribution, an 8-element array of uint32s holding the seed, and a 2-element array of uint64 that holds the 128-bit counter (<code>low, high</code>). The elements of the seed are the value provided by the user. Typical values for number of rounds are 4, 8, 12, or 20 (for high security).</p><p>ChaCha is seeded using a vector of 4 64-bit unsigned integers. By default this is provided by <a href="../SeedSequence/index.html#val-generate_64bit_state"><code>SeedSequence.generate_64bit_state</code></a>.</p></header><div class="odoc-content"><div class="odoc-spec"><div class="spec type anchored" id="type-t"><a href="#type-t" class="anchor"></a><code><span><span class="keyword">type</span> t</span></code></div><div class="spec-doc"><p><code>t</code> is the state of the bitgenerator.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-next_uint64"><a href="#val-next_uint64" class="anchor"></a><code><span><span class="keyword">val</span> next_uint64 : <span><a href="#type-t">t</a> <span class="arrow">-></span></span> <span class="xref-unresolved">Stdint</span>.uint64 * <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>next_uint64 t</code> Generates a random unsigned 64-bit integer and a state of the generator advanced forward by one step.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-next_uint32"><a href="#val-next_uint32" class="anchor"></a><code><span><span class="keyword">val</span> next_uint32 : <span><a href="#type-t">t</a> <span class="arrow">-></span></span> <span class="xref-unresolved">Stdint</span>.uint32 * <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>next_uint32 t</code> Generates a random unsigned 32-bit integer and a state of the generator advanced forward by one step.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-next_double"><a href="#val-next_double" class="anchor"></a><code><span><span class="keyword">val</span> next_double : <span><a href="#type-t">t</a> <span class="arrow">-></span></span> float * <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>next_double t</code> Generates a random 64 bit float and a state of the generator advanced forward by one step.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-initialize"><a href="#val-initialize" class="anchor"></a><code><span><span class="keyword">val</span> initialize : <span><span class="xref-unresolved">Bitgen__.Seed.SeedSequence.t</span> <span class="arrow">-></span></span> <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>initialize s</code> Returns the initial state of the generator. The random stream is determined by the initialization of the seed sequence <code>s</code> of <a href="../SeedSequence/index.html#type-t"><code>SeedSequence.t</code></a> type.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-initialize_full"><a href="#val-initialize_full" class="anchor"></a><code><span><span class="keyword">val</span> initialize_full : | ||
| <span><span class="label">key</span>:<span><span class="xref-unresolved">Stdint</span>.uint64 array</span> <span class="arrow">-></span></span> | ||
| <span><span class="label">counter</span>:<span>(<span class="xref-unresolved">Stdint</span>.uint64 * <span class="xref-unresolved">Stdint</span>.uint64)</span> <span class="arrow">-></span></span> | ||
| <span><span class="label">rounds</span>:int <span class="arrow">-></span></span> | ||
| <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>initialize_full key counter rounds</code> initializes the state of the ChaCha bitgenerator; where <code>key</code> is a 4-element array, <code>counter</code> is a 2-tuple, and <code>rounds</code> is the number of rounds to use. <code>rounds</code> must be non-negative, even and greater than 2, else an exception is raised.</p></div></div></div></body></html> | ||
| <span><span class="xref-unresolved">Bitgen__.Seed.SeedSequence.t</span> <span class="arrow">-></span></span> | ||
| <span><span>(<span class="xref-unresolved">Stdint</span>.uint64 * <span class="xref-unresolved">Stdint</span>.uint64)</span> <span class="arrow">-></span></span> | ||
| <span>int <span class="arrow">-></span></span> | ||
| <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>initialize_full seedseq counter rounds</code> initializes the state of the ChaCha bitgenerator; where <code>seedseq</code> is a <a href="../SeedSequence/index.html#type-t"><code>SeedSequence.t</code></a> used to initialize the PRNG's key array, <code>counter</code> is a 2-tuple used to initialize the 128-bit counter, and <code>rounds</code> is the number of rounds to use. <code>rounds</code> must be non-negative, even and greater than 2, else an <code>Invalid_argument</code> exception is raised.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-advance"><a href="#val-advance" class="anchor"></a><code><span><span class="keyword">val</span> advance : <span><span class="xref-unresolved">Stdint</span>.uint128 <span class="arrow">-></span></span> <span><a href="#type-t">t</a> <span class="arrow">-></span></span> <a href="#type-t">t</a></span></code></div><div class="spec-doc"><p><code>advance n</code> Advances the generator forward as if <code>n</code> calls to <a href="#val-next_uint32"><code>ChaCha.next_uint32</code></a> have been made, and returns the new advanced state.</p></div></div></div></body></html> |